Runtastic RUNBT1 Heart Rate Combo Monitor Compatible with iPhone 5s/5c/5 and iPhone 4s, Bluetooth Smart Ready Android devices running Android 4.3 & Samsung Galaxy S4 Allows heart rate data transmission without additional adapters via Bluetooth Smart technology Works with top-rated Runtastic Smartphone Apps for complete workout stats including heart rate zones and calories burned Transmits heart rate to indoor cardio equipment at health clubs and home gyms using 5.3 kHz technology Very low energy consumption, with a long-lasting battery that is easy to replace, and washable belt